This invention relates to a process and apparatus for use in the manufacturing of cigarette filters. More particularly, this invention relates to a process and an apparatus for high-speed filling of particulate matter in discrete cavities defined by adjacent individual filter plugs during the filter assembly operation.
In composite filters having cavities filled with particulate matter, the fill percentage of the cavities is very important. This is because, as the cigarette is placed into the mouth, it lies in a substantially horizontal plane. Thus, gravity draws the particulate matter down away from the top of the cavity. This creates an unprotected, unfiltered bypass above the particulate matter that does not inhibit the flow of smoke. The affect that this bypass has on the filtering capacity of a filter is not yet appreciated but can possibly be disproportionately large compared to the linear proportion of the width of the bypass to the width of the filter element. In fact, fluid flow principals dictate that fluid prefers to flow along a path of least resistance, thus indicating that the filtering efficiency of the particulate matter may be greatly reduced by the presence of any such pass through portion.
Referring to U.S. Pat. No 3,312,152 to Williamson, the content of which is incorporated herein by reference, an apparatus is described which attempts to fill the filter cavities. The Williamson apparatus transfers particulate material into discrete spaces between filter plugs. However, the speed of operation of the apparatus is limited due to inefficiency of relying on gravity alone to fill the rapidly passing cavities.
A prior art machine such as that described in U.S. Pat. Nos. 4,063,494 and 5,908,030, the contents of which are incorporated by reference, includes gravity-fed, wheel-shaped receiving magazines that receive filter segments laid out adjacent to one another in a spaced apart relationship on a paper carrier strip. The loaded strip is then brought into an assembly or guide channel and toward a filling area where the paper is formed on wheels into a receiving trough. As described in U.S. Pat. No. 4,015,514 to Nichols, the content of which is incorporated by reference, a vacuum is applied across adjacent filter segments in an effort to promote the filling of the cavity. However, because both the spacing of the segments varies and the density of the cellulose acetate filters varies, it is impossible to fill the cavities with any consistency. This means that in order to ensure a minimum percentage of filling, the process must be set up to significantly overfill the cavities above this target level. The industry has compensated for this by not demanding a high fill percentage. In this manner, the process tolerates a very high variance provided that the target fill percentage is sufficiently high.
Further, despite the fact that the fill percentage demanded by industry is low, it is desirable to completely fill the cavity with granules. As explained above, this is because it has been shown that a cavity that is not completely filled allows smoke to bypass the particulate filling, thus failing to permit the particulate to remove the undesirable compounds in the smoke.
Further, overfill of the cavity or the escape of the particulate from the cavities may cause the particulate to adhere to the outer garniture or the paper carrier strip and thus become embedded near the surface of the final product, leaving an unsightly stain or mark.
What is needed is a process of completely filling filter cavities in a commercially practicable manner. More specifically, what is needed is a process and an apparatus to rapidly fill active charcoal filter cavities at a rate exceeding 200 m/min.
A process of manufacturing composite filter stock is provided that includes several steps. In a first step, a paper carrier strip or garniture feeds along a conveyor. Along one edge of the carrier strip, the paper is folded back against itself. Fibrous filter segments are then deposited on the carrying strip in spaced apart intervals. The spacing defines cavities between adjacent filter segments. The carrier strip with the deposited filter segments is fed along a path of travel into an elongated guide or support chamber that substantially surrounds the circumference of the paper-enveloped segments and which leaves a narrow fill opening opposite a particulate filling opening that is elongated in the direction of motion of the carrying strip. Suction or a vacuum is concurrently applied adjacent the narrow opening, the suction increasing a downward momentum of a gravity feed stream of particulate matter and concurrently vacuuming away loose particulate matter. The cavities are concurrently filled with the particulate matter over a length corresponding to a predetermined path of travel of the carrying strip. The folded over edge is then unfolded and adhered to seal the fill opening. Alternately, a sealing strip seals the opening, thus encapsulating the filter segments and particulate matter. The filter stock is then cut to length, the cutting being registered to create discrete composite filter segments.
In another feature, filter cavities may be rapidly and completely filled with particulate matter such as charcoal.
In another feature, the density of activated charcoal is controlled through the introduction of an inactive filler material.